Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as a "head crash." Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as "texturing." Conventional texturing techniques involve mechanical polishing or laser texturing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer, a magnetic layer, a protective overcoat, and a lubricant topcoat, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers. The surface of an underlayer can also be textured, and the texture substantially replicated in subsequently deposited layers.
A typical longitudinal recording medium is depicted in FIG. 1 and comprises a substrate 10, such as an aluminum (Al)-alloy, e.g., an aluminum-magnesium (Al--Mg)-alloy, plated with a layer of amorphous nickel-phosphorus (NiP). Alternative substrates include glass, glass-ceramic materials and graphite. Substrate 10 typically contains sequentially deposited on each side thereof a chromium (Cr) or Cr-alloy underlayer 11, 11', a cobalt (Co)-base alloy magnetic layer 12, 12', and a protective overcoat 13, 13' thereon. Conventional protective overcoats can comprise various materials, such as carbon, silicon dioxide, hydrogenated carbon, or nitrogenated carbon. A lubricant topcoat 14, 14' is normally bonded to the protective overcoat. Cr underlayer 11, 11' can be applied as a composite comprising a plurality of sub-underlayers 11A, 11A'. Cr underlayer 11, 11', Co-base alloy magnetic layer 12, 12' and protective overcoat 13, 13', are usually deposited by sputtering techniques performed in an apparatus containing sequential deposition chambers. A conventional Al-alloy substrate is provided with a NiP plating, primarily to increase the hardness of the Al substrate, serving as a suitable surface to provide a texture, which is substantially reproduced on the disk surface.
In accordance with conventional practices, the lubricant topcoat is uniformly applied over the protective overcoat to prevent wear between the disk and head interface during drive operation. Excessive wear of the protective overcoat increases friction between the head and disk, thereby causing catastrophic drive failure. Excess lubricant at the head-disk interface causes high stiction between the head and disk. If stiction is excessive, the drive cannot start and catastrophic failure occurs. Accordingly, the lubricant thickness must be optimized for stiction and friction.
A conventional material employed for the lubricant topcoat comprises a perfluoro polyether (PFPE) which consists essentially of carbon, fluorine and oxygen atoms. However, as employed herein, the expression "perfluoro polyether" encompasses groups which are not completely perfluorinated, such as where the terminal methylene groups attached to hydroxyl radicals contain no fluorine. The lubricant is usually dissolved in an organic solvent applied and bonded to the magnetic recording medium by techniques such as thermal treatment, ultraviolet (UV) irradiation and soaking. A significant factor in the performance of a lubricant topcoat is the bonded lube ratio which is the ratio of the amount of lubricant bonded directly to the magnetic recording medium to the amount of lubricant bonded to itself or mobile lubricant. The degree of direct bonding or bonded lube ratio is dependent upon the particular material employed for the protective overcoat and the lubricant end-group. Desirably, the bonded lube ratio should be able to be controlled to realize a meaningful improvement in stiction and wear performance of the resulting magnetic recording medium.
In view of the criticality of the lubricant topcoat in magnetic recording media, there is a continuing need for improved uniform and controlled bonding of the lubricant topcoat to the magnetic recording medium, particularly to a protective overcoat. There is also a need for improved lubricants for use as topcoats in the manufacture of magnetic recording media capable of bonding to various protective overcoat materials in a controlled lube ratio.